Bioequivalence and Bioavailability Forum • Spaghetti & other pasta

Spaghetti & other pasta [NCA / SHAM]

posted by Helmut – Vienna, Austria, 2013-05-24 03:24 (3989 d 05:27 ago) – Posting: # 10635
Views: 17,135

Dear Yung-jin!

❝ Now I think that I have fully understood the differences between the linear and the lin-up/log-down method for AUC calculations.

Hhm.

❝ Actually, lin-up/log-down method is still a kind of data smoothing approach.

No, it isn’t.

❝ The key point is that involved calculation step still uses the raw data to calculate the interpolated data.

There is no interpolation done at all. Have a look at my example in the previous post. I gave the interpolation/imputation formulas only as a hint what might happen if we need an intermediate data point. If we want to calculate the area in the interval [t₂, t₂] no interpolation, smoothing, whatsoever is done. Both methods are straightforward:

linear: AUC_t1→t2=0.5(t₂–t₁)(C₂+C₁)

linlog: AUC_t1→t2=(t₂–t₁)(C₂–C₁)/log(C₂/C₁)

❝ As we can see, the errors between linear and lin-up/log-down become significantly apparent, especially when sampling time between two data points is getting greater.

Right.

❝ Therefore, when there is missing data occurring, the lin-up/log-down method shows more accurate than the linear.

Xactly. See also Nathan’s PK/PD Blog.

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Complete thread:

handling of missing data gracehung 2013-05-20 07:35
- Lin-up/log-down trapezoidal avoids most trouble Helmut 2013-05-20 14:22
  - Lin-up/log-down trapezoidal avoids most trouble yjlee168 2013-05-22 08:25
    - Multiple peaks: fallback to linear trapezoidal Helmut 2013-05-22 20:25
      - Multiple peaks: fallback to linear trapezoidal yjlee168 2013-05-22 21:57
        
        No interpolation Helmut 2013-05-22 23:25
        
        No interpolation yjlee168 2013-05-23 11:43
        
        Spaghetti & other pasta Helmut 2013-05-23 15:15
        
        Spaghetti & other pasta yjlee168 2013-05-23 20:47
        
        Spaghetti & other pasta Helmut 2013-05-23 21:29
        
        Spaghetti & other pasta yjlee168 2013-05-23 22:46
        
        Spaghetti & other pastaHelmut 2013-05-24 01:24
        
        Spaghetti & other pasta yjlee168 2013-05-24 09:17
        
        No interpolation Ken Peh 2013-05-30 19:55
        
        Different algos! Helmut 2013-05-30 22:38
        
        Different algos! Ken Peh 2013-06-03 17:52
        
        Calculate what? Helmut 2013-06-03 18:11
    - Lin-up/log-down trapezoidal example Helmut 2013-05-25 15:09
      - Lin-up/log-down trapezoidal example yjlee168 2013-05-25 19:45
- handling of missing data Ohlbe 2013-05-20 21:45
  - Sorry Helmut 2013-05-21 13:53
    - Sorry gracehung 2013-05-23 01:06
      - Uncertain time point Helmut 2013-05-23 01:35